Treatment of cellulose mixed esters



Patented Feb. 27, 1945 OFCELLULOSE MIXED ESTERS' TREATMENT Howard A.Tanner, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester,N. Y.,

a corporation of New Jersey No Drawing. Application March 14, 1941,

Serial N0. 383,369

13. Claims, (Ql. 106-171) This invention relates to the manufacture oisheeting and photographic film base and more particularly to a method oftreating cellulose mixed organic acid esters employed as the base of\thesheeting and film base whereby the adhesion of the sheet or film isreduced, and whereby no viscosity change is produced in the solutionfrom which the sheet or film base is coated.

Photographic films and similar films and thin sheeting commonly employedfor wrapping materials are usually prepared from cellulose esters bycoating 2. solution of the cellulose ester onto a smooth coating surfaceand then stripping oil? the film or sheet after the solvents have beenpartially evaporated. In the case of single esters no great diflicultyhas been experiencedin stripping the formed film or sheet from thecoating surface. However, when cellulose mixed organic acid esters werecoated from solvent solutions and in particular from chlorinatedsolvents in accordance with the gel dope process described in Fordyceapplication Serial No. 245,023, filed December-10, 1938, now U. S.Patent No. 2,319,055, issued May 11, 1943, appreciable difficulty wasexperienced from time to time with the adhesion of the sheet or film tothe coating surface. In some instances such adhesion caused particles ofthe film to be pulled away or the film to be torn with the result thatthe product was unusable.'

Various attempts were made to overcome this adhesion of the mixed estersheets. It was finally found that if the mixed ester were treated withan aqueous sodium or potassium soap solution that the adhesivecharacteristic of the resuiting-film base or sheet. could be controlled.However, if the soap treated mixed ester were made into a coatingsolution in a chlorinated solvent, the improvement in adhesive controlwas oflset by a persistent drift in solution viscosity. It was foundthat on standing the solution would gradually turn to. a gel. Thisviscosity change greatly interfered with production of sheets by theabove mentioned gel dope process. This is a phenomenon which isfrequently encountered The instant application describes an improvedmethod whereby a soap treatment may be employed to control theadhe'siveness or the cellulose mixed ester sheets as'well astheviscosity of the coating solution particularly when employingchlorinated solvents.

An object of the present invention is a method of reducing the inherentsticking tendency of films, foils and sheets made of cellulose mixedorganic acid esters.

Another object of the invention is a method for reducing the adherenceof cellulose mixed ester sheets to sheet forming surfaces.

A further object of the invention is a method of reducing the adherenceof cellulose mixed ester sheets and film base without producing atendency for viscosity increases in the solution from which the sheet orfilm base is coated.

In accordance with the invention these and other objects are attained bysoaking the cellulose mixed organic acid ester in an aqueous sodium orpotassium soap solution to thoroughly wet the ester with the soapsolution. The soap solution is then drained of! and the ester rinsed indistilled water to remove all but a minor per 1 cent of the sodium orpotassium soap solution. The washing is carried out sufficiently that nomore than 1%. preferably no morethan 0.5% of the soap remains in thecellulose ester. Ordinarily at least 0.1 oi. soap is retained by thecellulose ester aftengthe washing operation. The mixed ester is nowwashed with artificially hardened water containing one or more solublesalts of when alkalimetal salts (such as sodium stearate) V are .presentin solutions of cellulose esters in soldyents containing chlorinatedhydrocarbons. The

alkali metal ion evidently initiates or catalyzes a breakdown of thechlorinated solvent liberating acidic materials which cause the ester todecompose. This eflect may be prevented by the addition of small amountsot'a weakly acidic material such as stearic acid or boric acid torepresilhe formation of alkali metal ions.

metals such as calcium, magnesium, zinc, aluminum and copper therebychanging the residual sodium or potassium soap to the correspondingmetal soap which is insoluble and of weaker basicity than soaps ofpotassium. The ester is then drained free of th'giartificially hard enedwater and thoroughly rinsed with distilled water to remove the solublesodium or potassium.

salts. .This leaves only minor quantities of insoluble metal soaps inthe ester which do not react with chlorinated solvents to increase thesolution viscosity or cause it to gel. The ester is then dried and mixedin a solvent to form a cellulose mixed organic acid ester coating solution. The solution may then be coated by the process disclosed inFordyceet al. application Serial No. 335,336, filed May 15, 1940,-now'PatentNo. 2,295,394, into films and sheeting. ifthe solvent is a chlorinatedsolvent of the type described therein, or by the process described inDavidson Patent 2,051,201 it the solvent is acetoneor other suchnon-chlorinated solvent.

I have found that by the instant method a sheet or film of a greatlyreduced adherence tendency may be made. The product is of good clarity,has a pleasant smooth feel, and slides easily over itself or othersurfaces and will freely strip from the coating surface. Whenchlorinated solvents are employed there is no viscosity change over longperiods of time.

The soap solution is preferably a pure dilute solution of sodiumstearate soap or a similar soap such as sodium or potassium palmitateand pieate. The concentration of soap in the soap solution does notappear critical and may be in the range of approximately .05 to Thesoaking treatment may vary from fifteen minutes to several hours.Ordinarily the temperature of the A soap solution may be that ofthe roomalthough it may be raised somewhat, if desired. If chlo rinated solventsare employed the final washing is generally continued until only 0.1 to0.2% of invwsoluble' metal soap, based on the weightof the cellulosemixed ester, remains heldby the mixed ester.

The following are typical examples of how my invention may be applied informing thin sheetin! or film base but are not to be considered aslimitations thereof.

Example I A cellulose acetate butyrate containing 19% acetyl and 27%butyryl was repeatedly .washed with distilled water after which theacetate butyrate was covered with distilled water and boiled for severalhours. It was then again washed several times after which it was coveredwith 20 times its weight of distilled water and given a soap treatment.This involved heating the water to about 140-150 R, and then adding withstirring a quantity of warm (150 F.) l0% soap solution to result in aconcentration of .05.l% sodium stearate in the water. After one hour at;

tained at a temperature of 140 F. This results in a double decompositionreaction and the residual sodium stearate left in the mixed ester istransformed to insoluble aluminum stearate and the sodium combines withthe chloride. The water is then drained off and the mixed ester iswashed thoroughly with hot distilled water such as described in Fordyceet a1. application Serial No. 335,336, new U. S. Patent Number2,295,394, issued Sept. 8, 1942, the film exhibited no tendency toadhere to the coating wheel and was easily stripped therefrom.

Example II ,The treated ester was dissolved in 85% propylene dichlorideand 15% methyl alcohol and coated on a clean glass surface. The curedfilm showed no adhesion to the glass surface and was easily strippedtherefrom. Portions of the solution not coated showed no tendency toincrease in viscosity or to gel.

Example 111 A cellulose acetate butyrate containing 31% acetyl and 15%butyryl was treated with the washing and soap treatment described inExample I with the exception that a 0.1% magnesium sulfate solution wasemployed in place of the aluminumchloride solution in which case theresidual sodium stearate is changed to insoluble magnesium sulfate andthe sodium removed as sodium sulfate. When thoroughly dried the esterwas put in solution in a solvent mixture of 300 parts of propylenechloride and 100 p rts of ethylene chloride by mixing the ingredientswith stirring at 70 C. The solution was then formed into film support bythe process and apparatus deand dried. The drying operation employed isto contrifuge the mixed ester, until it contains only about three timesits weight of water, after which it is placed ina drier and dried atabout 180 F. to a moisture content of approximately 0.5%.

For film manufacture, the cellulose, acetate butyrate thus-treated withthe soapsolutionwas dissolved ina solvent mixture consisting of byweight of propylene chloride and 10% methyl alcohol to a solvent ratioof about 6:1. Dibutyl phthalate was added as plasticizer to the extentof 25 parts for parts of cellulose ester. The dope Ml: prepared bymixing thoroughly at a somewhat elevated temperature such as scribed inFordyce application Serial No. 335,335, now Patent No. 2,295,280. Nodifliculty was exp'eriencedin stripping-the formed film from the coatingsurface. Portions of the solution not coated exhibited no viscosityincrease or gelation tendency.

Example IV -A cellulose acetate propionate containing 30% acetyl and14.5%. propionyl was treated accord ing to the'procedure shown inExample I. This ester was made into a coating solution in 600 parts byweight of a solvent mixture composed of 53% by weight of propylenechloride and 47% by weight of amyl alcohol and 10% triphenyl phosphatebased on the weight of the ester. When coated according to the processdescribed in Fordyce application Serial No. 335,335, now U. S. PatentNumber 2,295,280, issued September 8, 1942, no appreciable adherence ofthe film to the coating wheel was noted. The viscosity of this solutiondid not-increase on standing.

A small percentage of the insoluble soap based.

solution after the ester and solvent have been .mixed will not producethe same result as is obtained by soaking the ester itself in a solublesoap 1''. and was then filtered. It was found that even after prolongedstanding there was no tendency for the solution to increase in viscosityor to gel. when supplied to a film coating machine 2,370,332 withoutdiminishing other desirable character this case the solution should beformed into the sheeting soon after it is made up otherwise the solutionwill exhibit a. viscosity increase. Furthermore, if acetone or someother solvent which does not have a gelling action or at least as activea gelling action as do chlorinated solvents the hardened water wash maybe omitted and the reduction of the adhesiveness of the sheetby the soaptreatment will be obtained.

My invention is applicable toany suitable cel-' lulose mixed organicacid ester such as cellulose acetate propionate, and cellulose acetatebutyrate, cellulose propionate butyrate, cellulose acetate propionatebutyrate, cellulose acetate stearate, cellulose acetate palmitate,cellulose acetate laurate and the'like.

The salts employed to harden the distilled water may be aluminumchloride, stannous chloride, copper sulfate, zinc sulfate and magnesiumsulfate. The zinc and tin salts are less desirable since they seem tocause haze in the'sheeting.

In the accompanying claims the term sheeting" is meant to includesheeting such as that employed for wrapping purposes as well as thatemployed for photographic film base.

While I have found that potassium and sodium soaps are very satisfactoryfor use in carrying out this invention I may'in general employ any watersoluble soaps including ammonium soaps.

Iclaim:

l. The method of preparing a cellulose mixed organic acid ester coatingsolution which comprises treating the ester forming the base of thesolution with an aqueous soap solution selected from the groupconsisting of sodium and potassium soap. solutions, washing thesoap'from the ester with distilled water until 0.1 to 1% of soap basedon the weight of the ester remains, treating the ester with artificiallyhardened water con taining soluble salts of one or more metals selectedfrom the group consisting of calcium, magnesium, zinc, aluminum andcopper, washing the ester substantially free from the soluble alkalimetal salts, drying the ester and mixing the ester and a plasticizer ina solvent t form a solution;

2. The method of preparing a cellulose acetate butyrate coating solutionwhich comprises treating the ester forming the base of the solution withan aqueous soap solution selected from the. group consisting of sodiumand potassium soap- 3. The method of preparing a cellulose acetatepropionate coating solution which comprises treating the ester formingthe base of the solution with an aqueous soap solution selected from thegroup consisting of sodium and potassium soap solutions, washing thesoap from the ester with distilled water until 0.1 to 1% of soap basedon the weight of the ester remains, treating the ester with artificiallyhardened water containing soluble salts of one or more metals selectedfrom the group consisting of calcium, magnesium, zinc,

aluminum and copper, washing the ester substantially free from thesoluble alkali metal salts,

drying the ester and mixing the ester and a plasticizer in a solvent toform a solution.

4. The method of reducing the adhesive properties of a. cellulose mixedorganic acid ester without increasing its tendency to gain in viscositywhen in solution in organic solvents which comprises treating the mixedester with an aqueous soap solution, and washing the soap from the esterwith a solvent of the soap until 0.1 to 0.5% of soap based on the weightof the ester remains.

5. The method of reducing the adhesive properties of a cellulose mixedorganic acid ester without increasing its tendency to gain in viscositywhen in solutionin organic solvents which comprises treating the esterwith an aqueous soap solution selected from the group consisting of asodium soap solution and a potassium soap solution, washing the soapfrom the ester with distilled water until 0.1 to 1% of soap based on thesoluble salts of one or more metals selected from the group consistingof calcium, magnesium, zinc.

aluminum and copper, and washing the ester substantially free from thesoluble alkali metal salts.

6. Cellulose mixed organic acid ester sheeting containing 0.1 to 0.2% ofan insoluble metal soap therein.

9. Cellulose mixed organic acid ester sheeting taining 0.1-0.2% of amagnesium soap therein.

13. The method of reducing the adhesive properties of a cellulose mixedorganic ester without increasing its tendency to gain in viscosity whenin solution in organic solvents, which comprises treating the mixedester with an aqueous soap solution, and washing the soap from the esterwith distilled water until 0.1-0.5% of soap, based on the weight of theester, remains.

HOWARD A.

